The Fix
pip install celery==4.4.0rc5
Based on closed celery/celery issue #5466 · PR/commit linked
Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.
@@ -47,6 +47,36 @@ class SchedulingError(Exception):
+class BeatLazyFunc(object):
+ """An lazy function declared in 'beat_schedule' and called before sending to worker
+
Option A — Upgrade to fixed release\npip install celery==4.4.0rc5\nWhen NOT to use: Do not use this fix if the callback function is not intended for delayed execution.\n\n
Why This Fix Works in Production
- Trigger: - [ ] I have included all related issues and possible duplicate issues
- Mechanism: The beat_schedule parameter did not support a callback function for delayed execution
- Why the fix works: Adds a delay parameter function to the beat_schedule, allowing for lazy function execution before sending to the worker. (first fixed release: 4.4.0rc5).
- If left unfixed, retries/timeouts can trigger duplicate external side-effects (double charges, duplicate emails, repeated writes).
Why This Breaks in Prod
- The beat_schedule parameter did not support a callback function for delayed execution
- Production symptom (often without a traceback): - [ ] I have included all related issues and possible duplicate issues
Proof / Evidence
- GitHub issue: #5466
- Fix PR: https://github.com/celery/celery/pull/5558
- First fixed release: 4.4.0rc5
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.76
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“can you come with a PR with proper testcase?”
“> can you come with a PR with proper testcase? which branch could I commit to？”
“https://github.com/celery/celery/pull/5558”
“class BeatCallBack(object): def __init__(self, func, *args, **kwargs): self._func = func self._func_params = { "args": args, "kwargs": kwargs } def __call__(self): ret = self._func(*self._func_params["args"], **self._func_params["kwargs"]) info("beat…”
Failure Signature (Search String)
- - [ ] I have included all related issues and possible duplicate issues
- or possible duplicates to this issue as requested by the checklist above.
Copy-friendly signature
Failure Signature
-----------------
- [ ] I have included all related issues and possible duplicate issues
or possible duplicates to this issue as requested by the checklist above.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
- [ ] I have included all related issues and possible duplicate issues
or possible duplicates to this issue as requested by the checklist above.
What Broke
Tasks scheduled via beat_schedule could not execute delayed functions, causing unexpected behavior.
Why It Broke
The beat_schedule parameter did not support a callback function for delayed execution
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==4.4.0rc5
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/celery/celery/pull/5558
First fixed release: 4.4.0rc5
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use this fix if the callback function is not intended for delayed execution.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
- Pin production dependencies and upgrade only with a reproducible test that hits the failing path.
Version Compatibility Table
| Version | Status |
|---|---|
| 4.4.0rc5 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.